It is known that hollow electrodes comprise an electrode body proper and an inner pipe forming an electrode channel through which the furnace is charged.
The advantages of charging furnaces through hollow electrodes are well-known. However, in the course of the furnace operation some problems arise. One of these lies in the fact that the electrodes are continuously moved vertically to control the electric power of the furnace and, as the electrodes are being consumed, they are lowered and additional lengths are added i.e. they are built-up over certain time intervals dependent on the furnace operating conditions. When the electrodes are built-up the electrode inner pipe is built-up, too. To accomplish the addition of lengths or building-up of the inner pipe, the charging of the furnace must be stopped and the inner pipe closed, due to the fact that toxic gases are emitted from the furnace.
To close the inner pipe shutters are now used which remain in the electrode and, ultimately, go into the melt together with the electrode.
The melting-down of this shutter requires the a constant replacement of shutters, which is not economical. In addition, the melting-down of undesirable materials (i.e. the shutters) contaminates the melt which is undesirable for the furnace operation.
These effects can be partially eliminated by a device for charging a furnace through an electrode inner pipe (c.f., see FRG patent No. 1257308 cl. F - 23k). This device comprises a casing with a side pipe for charging, and with coaxial holes one of which is provided in the bottom portion of the casing and is intended for putting the casing on the electrode inner pipe, and the other hole is provided in the upper portion of the casing and is tightly covered by a closing means to prevent the leakage of furnace gas. The closing means is in the form of an elastic plug secured on a long rod and positioned above or below the side pipe for intake of charge.
As charging of the furnace requires access to the electrode channel and to the sub-electrode space of the furnace for cleaning the channel or probing, the use of the plug which is permanently above it or in its upper portion prevents this access.
The long rod used for moving, compressing or extending said plug in the electrode channel causes difficulties in servicing. Furthermore, the case of repair and replacement of the plug it is necessary to open the channel. This inevitably involves emission of toxic furnace gases which can harm the operating personnel.